Press on Power-Up Detection for a Touch-Sensor Device

1. A method comprising: powering up an electronic system; measuring a first capacitance value of a target sensing device within a certain time period during the powering up of the electronic system, wherein a baseline value for the target sensing device is not established prior to the measuring the first capacitance value; measuring a second capacitance value of a secondary sensing device within the certain time period; determining that a conductive object was present at the target sensing device within at least the certain time period prior to establishing the baseline value for the target sensing device, wherein the determining comprises calculating a difference between the first capacitance value of the target sensing device and the second capacitance value of the secondary sensing devices exceeds a button threshold.

2. The method of claim 1 , wherein the target sensing device comprises a target touch-sensor button and the secondary sensing device comprises a secondary touch-sensor button.

3. The method of claim 2 , further comprising calculating an offset value for the target touch-sensor button and for the secondary touch-sensor button, wherein calculating the offset value comprises determining an offset value for the target touch-sensor button and for the secondary touch-sensor button, such that when the offset value is added to the first capacitance value, an adjusted capacitance value for the target touch-sensor button and the second capacitance value of the secondary touch-sensor button is approximately equal.

4. The method of claim 3 , further comprising establishing a baseline capacitance value of the target touch-sensor button, wherein the establishing the baseline capacitance value comprises applying the offset value of the target touch-sensor button to the first capacitance value of the target touch-sensor button.

5. The method of claim 3 , further comprising establishing a second baseline capacitance value of the secondary touch-sensor button, wherein the establishing the second baseline capacitance value comprises determining a lowest baseline capacitance value of the secondary touch-sensor button and of other secondary touch-sensor buttons.

6. The method of claim 3 , further comprising establishing a second baseline capacitance value of the secondary touch-sensor button, wherein the establishing the second baseline capacitance value comprises computing an average baseline capacitance value of the secondary touch-sensor button and of other secondary touch-sensor buttons.

7. The method of claim 1 , further comprising, when the conductive object is present at the power-up, updating a status register.

8. The method of claim 1 , further comprising, when the conductive object is present at the target sensing device within the certain time period, sending an interrupt request to a host processor.

9. The method of claim 1 , further comprising after the certain time period of the powering up of the electronic system, establishing the baseline value of the target sensing device when the conductive object is not present at the target sensing device.

10. The method of claim 9 , wherein establishing the baseline value of the target sensing device comprises: determining that the conductive object is no longer present at the target sensing device during a second time period after the certain time period; and measuring a third capacitance value of the target sensing device when the conductive object is not longer present at the target sensing device.

11. An electronic system comprising: A processing device configured to receive signals from a target sensing device and one or more secondary sensing devices, the processing device to determine at power-up of the electronic system that a conductive object is present at the target sensing device within a certain time period during the power-up by determining that a difference between a first capacitance value of the target sensing device and a second capacitance value of one or more secondary sensing devices exceeds a button threshold prior to establishing a baseline value for the target sensing device.

12. The apparatus of claim 11 , wherein the processing device comprises one or more capacitance sensors coupled to the target sensing device, and wherein the one or more capacitance sensors are configured to measure a capacitance on the target sensing device to detect the presence of the conductive object on the target sensing device.

13. The apparatus of claim 11 , wherein the signals received from the target sensing device represent the capacitance measured on the target sensing device.

14. The apparatus of claim 11 , wherein the target sensing device comprises a target touch-sensor button and the one or more secondary sensing devices are one or more secondary touch-sensor buttons.

15. The apparatus of claim 14 , wherein the processing device is configured to: measure the first capacitance value of the target touch-sensor button; and measure the second capacitance value of the secondary touch-sensor buttons.

16. The apparatus of claim 11 , further comprising an interface line coupled between the processing device and a host processor, the interface line to send instructions to update a status register on the host processor when the conductive object is present at the power-up.

17. An electronic system comprising: means for powering up the electronic system during a first time period; means for measuring a first capacitance value of a target sensing device within the first time period, wherein a baseline value for the target sensing device is not established prior to the measuring the first capacitance value; means for measuring a second capacitance value of a secondary sensing device within the first time period; means for determining that a conductive object was present at the target sensing device within at least the certain time period prior to establishing the baseline value for the target sensing device, wherein the means for determining comprises calculating that a difference between the first capacitance value of the target sensing device and the second capacitance value of the secondary sensing devices exceeds a button threshold.

18. The electronic system of claim 17 , wherein the means for determining during the first time period occurs before a second time period begins, the second time period comprising detecting when the conductive object is no longer present.